1. Field of the Invention
This invention relates to a flywheel device which is directly coupled to an electric generator provided with electrically activated starting means. More particularly, it relates to such a flywheel device according to which electrical energy is converted into and stored as an inertial energy of a rotating body, which inertial energy can be reconverted into and supplied as electrical energy whenever the occasion demands.
2. Description of the Prior Art
Certain prior art flywheel devices of the above described type are directly coupled to an electric generator operatively linked to a separate starting electric motor. Other flywheel devices of the same type are directly coupled to a motor-generator, i.e. a dynamoelectric device which may be employed selectively as the starting electric motor or as the electric generator through use of stationary thyristor starting means. In both of these cases, the diameter of the flywheel device is necessarily increased in order to achieve a large inertial effect so that the overall weight of the device occasionally reaches hundreds of tons.
Hence, the recent tendency is towards adopting a vertical shaft type device rather than a horizontal shaft type device, in order to avoid shaft flexure, save floor space, and to reduce excessive noise.
In the following description of the prior art device and a preferred embodiment of the present invention, the electric generator provided with electrically activated starting means is the dynamoelectric device or motor-generator defined above.
The conventional flywheel device which is directly coupled to the vertical shaft type motor-generator is shown in a longitudinal section in FIG. 1.
Referring to FIG. 1, the numeral 1 designates a motor-generator. The numeral 2 designates a rotor having a yoke attached to an intermediate shaft 3. To the circular outer periphery of the yolk of the rotor 2, there is attached a plurality of field poles. An upper shaft 4 is directly coupled to the intermediate shaft 3 and has attached thereto slip rings 5 adapted for conducting exciting current from an exterior exciter or thyristor starting device, not shown. A stator 6 is supported by a stator frame 8 and carries a stator winding on a stator iron core 7. An upper guide bearing 9 is supported by an upper bracket 10 and is adapted for radially supporting the upper shaft 4. An intermediate guide bearing 11 is supported by an intermediate bracket 12 and radially supports the intermediate shaft 3.
Directly coupled to the underside of the intermediate shaft 3 by any suitable means as by bolts is a flywheel device 13 which is comprised of a plurality of solid discs 14 clamped together by a plurality of tightening bolts 15.
A thrust collar 16 is attached to the lower end of the flywheel device 13. A thrust bearing 17 is adapted for carrying the total weight of a rotating portion consisting essentially of the rotor 2 and the flywheel device 13. In FIG. 1 the numeral 18 designates a lower guide bearing for radially supporting the thrust collar 16, the numeral 19 a lower bracket for supporting the lower guide bearing 18 and the thrust collar 16, and the numeral 20 a foundation of iron reinforced concrete.
In the operation of the motor-generator coupled flywheel device, the motor-generator 1 is started as the electric motor by the excitation current supplied from the thyristor starting device. In this manner, the flywheel device 13 is accelerated to its rated r.p.m. and thus a rotational inertial energy is stored in the device 13. The motor-generator 1 is operated as the electric generator whenever it becomes necessary to supply an electrical energy converted from the inertial energy.
Thus, in order to store a large energy, it is necessary to use a flywheel device of larger diameter and weight. In addition, since a unitary disc of a larger weight is extremely inconvenient with regard to transport and manufacture, the disc is divided into plural disc portions of smaller thickness stacked horizontally one upon the other.
On the other hand, rotation of the rotor 2 of the motor-generator 1 is deviated from rotation about the rotor axis to the extent that the surface of the flywheel device 13 disposed below the motor-generator 1 is deviated from the horizontal axis. Thus, it is required that each disc of the larger diameter and weight mass be machined within a narrow tolerance.
The prior art flywheel device has a drawback that, since the motor-generator 1 is mounted on the flywheel device 13, it is required that each flywheel disc 14 be machined within a narrow tolerance in order that the deviation of the rotor rotation from the rotation about the rotor axis be maintained within allowable limits, and that, even though each flywheel disc 14 could be machined within the narrow tolerance, it is not always possible to maintain the deviation of the general plane or surface of the flywheel disc 14 from the horizontal axis within allowable limits at the time that the discs 14 are stacked ultimately in position below the motor-generator 1.